Peritoneal dialysis involves introducing dialysis fluid into the peritoneal cavity of a subject. Conventionally, the dialysis fluid is introduced and removed batch wise (i.e., in cycles) to facilitate control of the dialysis process, i.e., to allow measurements to be performed on the dialysate as the procedure progresses, e.g., measurements of the volume of the dialysate introduced and removed from the subject.
It has been recognized in the art for some time that continuous flow of dialysate to and from the subject would improve the efficiency of peritoneal dialysis. For example, where a batch wise procedure typically passes 2 liters of dialysate through the peritoneal cavity in an hour, a continuous process will pass 18 liters in the same period of time. This passage of large volumes of dialysate means that substantially greater amounts of uremic toxins can be removed using the continuous approach as compared to the batch wise approach.
The continuous approach, however, runs the risk of a significant accumulation of fluid in the peritoneal cavity through ultrafiltration of the subject's bodily fluids into the dialysate. Alternatively, high levels of fluid can be absorbed into the subject's tissues, which is also potentially dangerous. Prior to the present invention, the only way to address these risks was to periodically stop the process and determine the amount of fluid in the peritoneal cavity by draining the fluid and measuring its volume. This, of course, defeats the goal of having a continuous process and makes the process less acceptable to the subject.
Prior workers in the art have considered using so called whole-body bioimpedance measurements to estimate the volume of fluid in the peritoneal cavity during batch wise peritoneal dialysis. See Rallison et al., “Errors in estimating peritoneal fluid by bioelectrical impedance analysis and total body electrical conductivity,” Journal of the American College of Nutrition, 12:66-72, 1993. These workers concluded that this measurement technique did not provide a reliable measurement of changes in fluid volume in the peritoneal cavity.
Significantly, this prior unsuccessful work did not involve continuous peritoneal dialysis where the need for fluid volume measurement is more critical than in a batch wise setting. In particular, in continuous peritoneal dialysis, one needs at least periodic and, preferably, a continuous measurement of changes in the volume of fluid in the peritoneal cavity to ensure the safety of the subject. Moreover, for the same reason, the measurement needs to be reliable.